1. Add ale.setup and ale.setup.buffer for pure Lua configuration.
2. Update many global settings to use Booleans instead of numbers to
make types easiert to work with in Lua.
3. Radically reformat documentation and fix errors to make
documentation more usable for Neovim users.
* Update dart analysis_server command
In 2021 the dart team added a new sub-command `language-server` to
replace the original `./snapshots/analysis_server.dart.snapshot --lsp`
convention for starting the language server.
https://github.com/dart-lang/sdk/commit/c224cc2e0d4cd8fc536c21ee963a0254d18a27bb
* Add ale_dart_analysis_server_enable_language_server option
This allows users to opt-in to the new `dart language-server` command.
* Enable ale_dart_analysis_server_enable_language_server option by default
* Update doc/ale-dart.txt
Include the dart version number where the `dart language-server` command
was added.
w0rp